Microbial photosynthetic and photoprotective pigments in Himalayan soils originating from different elevations and successional stages

Abstract

Soil microbes evolved complex metabolic strategies including photoprotective and photosynthetic pigments to survive the environmental stress including high UV irradiance, oscillating temperature and drought. Despite pigment importance for survival of soil microbes in alpine ecosystems, there have been few efforts documenting the soil pigment content, diversity and the dependence on microbial soil community, soil physico-chemical properties and constraining climatic factors. We examine how the composition and content of pigments in microbial soil communities in the Himalayas differ between major habitats spread across an elevation 4300–6000 m including cold deserts, steppes, alpine and subnival vegetation, and between several primary successional stages behind retreating glaciers, in relation to soil nutrient and water availability. Scytonemin was the prominent pigment across all of the studied habitats, followed by chlorophyll a, b; myxoxanthophyll and β-carotene. Rarely documented microbial pigments were also detected, including bacteriochlorophyll a and (2S,29S)-oscillol 2,29-di(a-l-fucoside). The contents of most of the investigated pigments showed a unimodal-shape relation to the cyanobacterial biomass. Pigments also differed in elevation optima. Alpine meadow soils had more diverse microbial and pigment assemblages than desert and steppe soils, or pioneer soils developing behind retreating glaciers. Pigments also varied across primary succession, with most pigments having a mid-successional peak. The best soil chemical predictors of pigment compositional variation were total nitrogen and cation contents. Our results shed light on the pigment composition and content in soil microbial assemblages and bring new information on ecological drivers influencing the production of photoprotective and photosynthetic pigments in Himalayan soils.